The present invention relates to a device and a method for redirecting a leakage current flowing between a stator and a rotor, which can be used for example in conjunction with an axial compressor. The invention furthermore relates to a rotor as well as a compressor comprising a corresponding device.
Gas turbines can have a compressor in which a rotor may rotate in relation to a stationary stator. In order to minimize leakage currents between the rotating rotor and an inner cover band of the stationary stator, a sealing arrangement designated as an “inner air seal” may be used. In spite of such a sealing arrangement, a relatively small quantity of air flowing back under the inner cover bands of the compressor stators cannot be avoided. The re-entry of this low-energy leakage mass flow into the main channel of the compressor causes a thickening of the hub boundary layer. As a result, the stability of the compressor and its efficiency are impaired.
In order to reduce this detrimental effect from the leakage mass flow, efforts may be made to minimize the mass flow. To this end, more effective sealing systems may be installed. However, a minimal leakage is necessary and unavoidable so that the rotor does not heat up too much.
It is therefore the objective of the present invention to make available a device and a method for redirecting a leakage current flowing between a stator and a rotor, which is able to reduce the undesired effects of the leakage current. Moreover, it is the objective of the present invention to make available a compressor with a corresponding device.
The present invention is based on the knowledge that the detrimental effects of the leakage mass flow may be reduced or avoided if the leakage current is blown off further upstream from the stator. As a result, the leakage current has more time to intermix with a main flow before it reaches the stator. In this way, it is possible to flow against the stator with a healthier boundary layer. Furthermore, the approach according to the invention offers the possibility that the leakage current may be injected into the main current with greater energy, wherein the injection direction can be varied and optimized. As a result, the intermixing may be improved and the hub boundary layer may become thinner. In addition, the pulsating flow may have a stabilizing effect on the stator.
According to the invention, the detrimental effects of the leakage flows in the area of the inner air seals can be reduced, in that the leakage flows are re-introduced further upstream. In this way, the re-entry of the leakage mass flow may be optimized such that the re-entry does not occur in the gap between the rotor platform and the stator platform.
A device according to the invention for redirecting a leakage current flowing between a stator and a rotor includes a sealing element for interrupting the leakage current, an outlet opening disposed on the rotor and a guide which is configured to direct the leakage current past the sealing element to the outlet opening.
In an advantageous embodiment of the device according to the invention, the guide may be configured to provide a defined injection direction for the leakage current at the outlet opening. By specifying a defined injection direction, it is possible to optimize the intermixing of the leakage current with the main flow.
Furthermore, the guide may have a channel leading through a rotor platform of the rotor, which channel is connected to the outlet opening. It is possible to easily integrate the channel into an existing rotor platform. In addition, a desired outflow direction and outflow energy for the leakage current may be adjusted through the channel.
For example, the outlet opening may be disposed in a rotor platform of the rotor. As a result, it is possible for the leakage current to blow off upstream from the stator.
In an advantageous embodiment of the device according to the invention, the rotor may have an extension, which is configured to bridge a gap extending in the radial direction between the rotor and stator, wherein the sealing element may be disposed on a stator-side end of the extension. It is possible to prevent a re-entry of the leakage current into the gap between rotor and stator in this way.
The guide may be configured to direct the leakage current to go along between a rotor shaft of the rotor and the extension. Thus, a radially lower area of the extension may serve as a guide for the leakage current.
For example, the sealing element may abut an inner cover band of the stator, wherein a distance of the sealing element to a radially outer end of the inner cover band is greater than or equal to a distance of the sealing element to a radially inner end of the inner cover band.
Alternatively, the sealing element may abut an inner cover band of the stator, wherein a distance of the sealing element to a radially outer end of the inner cover band is less than a distance of the sealing element to a radially inner end of the inner cover band.
In an advantageous embodiment of the device according to the invention, the outlet opening may be disposed in a hub surface and/or a front surface of the rotor. This makes it possible to realize an advantageous injection of the leakage current.
In doing so, a distance of the outlet opening from an edge of the hub surface facing away from the stator may be greater than a distance of the outlet opening from an edge of the hub surface facing the stator.
For example, the outlet opening may also be disposed on an edge of the hub surface facing the stator.
Furthermore, the outlet opening may be disposed between two rotor blades of the rotor, wherein the outlet opening may be disposed closer to the one of the two rotor blades which, in relation to a rotational direction of the rotor, is disposed behind the outlet opening.
For example, the outlet opening may have a round cross section. This type of cross section may be realized in a simple manner by a borehole.
Alternatively, the outlet opening may be configured as a slot. Such a formation may be advantageous for example if the outlet opening is disposed on the edge of the rotor platform.
In an advantageous embodiment of the device according to the invention, the device may comprise at least one other outlet opening disposed on the rotor and at least one other guide, wherein the at least one other guide is configured to direct at least a portion of the leakage current past the sealing element to the at least one other outlet opening. As a result, a re-entry of the leakage current can be distributed uniformly.
A rotor according to the invention may comprise a device according to the above. In this way, the device according to the invention may be combined with a rotor or be integrated into the rotor.
A compressor according to the invention may comprise a rotor according to the invention and a stator, wherein the rotor is disposed upstream of the stator in relation to a main flow in the compressor. As a result, the approach according to the invention can be used advantageously in conjunction with compressors such as those used in gas turbines for example.
A method according to the invention for redirecting a leakage current flowing between a stator and a rotor has a step of interrupting the leakage current with a sealing element and a step of directing the leakage current past the sealing element to an outlet opening disposed on the rotor.
Additional advantages, features and details of the invention are disclosed in the following description of a graphically depicted exemplary embodiment.